CT focal point determination method and system

ABSTRACT

A method for determining a CT focal point includes determining a first intensity of first radiation incident on a first detector unit of a scanner, wherein the scanner may include a non-uniform anti-scatter grid (ASG) and a radiation source, and the non-uniform ASG may be configured according to a first focal point of the radiation source. The method also includes determining a second intensity of second radiation incident on a second detector unit of the scanner, wherein the first radiation and the second radiation are emitted from the radiation source with a second focal point. The method further includes determining a displacement of the second focal point from the first focal point based on the first intensity and the second intensity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/719,990 filed on Sep. 29, 2017, which is a continuation ofInternational Application No. PCT/CN2017/099899 filed on Aug. 31, 2017,the entire contents of which are incorporated herein by reference.

FIELD

The present disclosure generally relates to a technical field of a CTscanner, and more particularly to a focal point determining method andsystem for determining the focal point of a radiation source of a CTscanner.

BACKGROUND

During a scanning performed by a computed tomography (CT) scannerequipped with anti-scatter grids (ASGs), the displacement of the focalpoint of the radiation source of the CT scanner may cause a portion ofthe radiation emitted by the radiation source intended to be received bythe detector of the CT scanner blocked by the ASGs, causing a reductionof the quality of the image generated based on the scanning. Varioushardware related (e.g., focus point tracing) or software related (e.g.,image post-processing) techniques may be adopted for compensating theimage quality reduction. However, the displacement of the focal pointneeds to be determined for most of these techniques. There is a need fora method of low cost and high reliability for determining thedisplacement of the focal point during the scanning of the CT scanner.

SUMMARY

According to an aspect of the present disclosure, a method may includedetermining a first intensity of first radiation incident on a firstdetector unit of a scanner. The scanner may include a non-uniformanti-scatter grids (ASG) and a radiation source, and the non-uniform ASGmay be configured according to a first focal point of the radiationsource. The method may also include determining a second intensity ofsecond radiation incident on a second detector unit of the scanner,wherein the first radiation and the second radiation are emitted fromthe radiation source with a second focal point. The method may furtherinclude determining a displacement of the second focal point from thefirst focal point based on the first intensity and the second intensity.

In some embodiments, the determining the displacement may comprisedetermining a ratio of the first intensity to the second intensity; anddetermining the displacement based on the ration.

In some embodiments, the method may further comprising determining acorrelation between the displacement and the ratio using a pinholepositioned between the radiation source and a detector of the scanner,the detector including the first detector unit and the second detectorunit, wherein the displacement is determined further based on thecorrelation

In some embodiments, the method may further include generating, based onthe displacement, a calibration instruction for calibrating the scanner.

In some embodiments, the method may further include obtaining scan databy controlling the scanner to scan a subject, and generating an imagebased on the scan data and the displacement.

In some embodiments, the first radiation and the second radiation may beemitted during the obtaining the scan data.

In some embodiments, the non-uniform ASG may include at least one firstcell. The first detector unit and the second detector unit may beincluded in the first cell.

In some embodiments, the non-uniform ASG may include at least one secondcell and at least one third cell having different structures. The secondcell and the third cell may include plates of different heights. Thefirst detector unit may be included in the second cell, and the seconddetector unit may be included in the third cell.

In some embodiments, the method may further include obtaining at leastone parameter relating to the non-uniform ASG, wherein the displacementis determined based at least in part on the at least one parameter.

In some embodiments, the at least one parameter may comprise at leastone of a height of at least a portion of the non-uniform ASG and adistance from the second focal point to a top of the at least a portionof the non-uniform ASG.

According to another aspect of the present disclosure, a system mayinclude at least one processor and at least one storage device storinginstructions. When executing the instructions, the at least oneprocessor may be configured to cause the system to determine a firstintensity of first radiation incident on a first detector unit of ascanner, wherein the scanner may include a non-uniform anti-scattergrids (ASG) and a radiation source, and the non-uniform ASG may beconfigured according to a first focal point of the radiation source. Theat least one processor may also be configured to cause the system todetermine a second intensity of second radiation incident on a seconddetector unit of the scanner, wherein the first radiation and the secondradiation may be emitted from the radiation source with a second focalpoint. The at least one processor may further be configured to cause thesystem to determine a displacement of the second focal point from thefirst focal point based on the first intensity and the second intensity.

According to yet another aspect of the present disclosure, ananti-scatter grid for determining a focal point of a radiation source ofa scanner may include a plurality of plates defining a plurality ofcells. The plurality of cells may include at least one first cell. Afterthe anti-scatter grid being installed on a detector of the scanner, thefirst cell may include a first detector unit and a second detector unitof the detector.

In some embodiments, the first detector unit and the second detectorunit may be adjacent to one another.

In some embodiments, each of the plurality of cells of the anti-scattergrid have a same configuration as the first cell.

According to yet another aspect of the present disclosure, ananti-scatter grid for determining a focal point of a radiation source ofa scanner may include a plurality of plates defining a plurality ofcells. The plurality of cells may include at least one second cell andat least one third cell. The second cell and the third cell may includeplates of different heights. The second cell and the third cell may havedifferent structures. After the anti-scatter grid being installed on adetector of the scanner, the second cell may include a first detectorunit of the detector, and the third cell may include a second detectorunit of the detector.

In some embodiments, the second cell and the third cell may be adjacentto one another.

Additional features will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the artupon examination of the following and the accompanying drawings or maybe learned by production or operation of the examples. The features ofthe present disclosure may be realized and attained by practice or useof various aspects of the methodologies, instrumentalities andcombinations set forth in the detailed examples discussed below.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present disclosure is further described in terms of exemplaryembodiments. These exemplary embodiments are described in detail withreference to the drawings. These embodiments are non-limiting exemplaryembodiments, in which like reference numerals represent similarstructures throughout the several views of the drawings, and wherein:

FIG. 1-A is a schematic diagram illustrating an exemplary CT systemaccording to some embodiments of the present disclosure;

FIG. 1-B is a schematic diagram illustrating an exemplary structure andmechanism of a CT scanner according to some embodiments of the presentdisclosure;

FIG. 2-A is a schematic diagram illustrating exemplary hardware and/orsoftware components of an exemplary computing device on which theprocessing engine may be implemented according to some embodiments ofthe present disclosure;

FIG. 2-B is a schematic diagram illustrating exemplary hardware and/orsoftware components of an exemplary mobile device on which the terminalmay be implemented according to some embodiments of the presentdisclosure;

FIG. 3 is a schematic diagram illustrating an exemplary processingengine according to some embodiments of the present disclosure;

FIG. 4-A is a schematic diagram illustrating the effect of the change ofthe focal point of the radiation source in the CT scanner;

FIGS. 4-B, 4-C and 4-D are schematic diagrams illustrating exemplarynon-uniform ASGs according to some embodiments of the presentdisclosure;

FIG. 5 is a schematic diagram illustrating an exemplary process fordetermining the focal point of the radiation source according to someembodiments of the present disclosure;

FIG. 6 is a schematic diagram illustrating an exemplary process fordetermining the displacement of the focal point based on the firstintensity and the second intensity according to some embodiments of thepresent disclosure;

FIGS. 7-A and 7-B are schematic diagrams of the process illustrated inFIG. 6 according to some embodiments of the present disclosure;

FIG. 8 is a schematic diagram illustrating an exemplary process fordetermining the displacement of the focal point based on the firstintensity and the second intensity according to some embodiments of thepresent disclosure;

FIGS. 9-A and 9-B are schematic diagrams illustrating exemplarytechniques for generating the correlation between the ratio of the firstintensity to the second intensity and the displacement of the focalpoint according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is directed to determine a focal point of theradiation source of a CT scanner equipped with a non-uniform ASG duringthe scanning performed by the CT scanner.

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant disclosure. However, it should be apparent to those skilledin the art that the present disclosure may be practiced without suchdetails. In other instances, well known methods, procedures, systems,components, and/or circuitry have been described at a relativelyhigh-level, without detail, in order to avoid unnecessarily obscuringaspects of the present disclosure. Various modifications to thedisclosed embodiments will be readily apparent to those skilled in theart, and the general principles defined herein may be applied to otherembodiments and applications without departing from the spirit and scopeof the present disclosure. Thus, the present disclosure is not limitedto the embodiments shown, but to be accorded the widest scope consistentwith the claims.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a”, “an”, and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise”,“comprises”, and/or “comprising”, “include”, “includes”, and/or“including”, when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

It will be understood that the term “system,” “unit,” “module,” and/or“block” used herein are one method to distinguish different components,elements, parts, section or assembly of different level in ascendingorder. However, the terms may be displaced by other expression if theyachieve the same purpose.

Generally, the word “module,” “sub-module,” “unit,” or “block,” as usedherein, refers to logic embodied in hardware or firmware, or to acollection of software instructions. A module, a unit, or a blockdescribed herein may be implemented as software and/or hardware and maybe stored in any type of non-transitory computer-readable medium orother storage device. In some embodiments, a software module/unit/blockmay be compiled and linked into an executable program. It will beappreciated that software modules can be callable from othermodules/units/blocks or from themselves, and/or may be invoked inresponse to detected events or interrupts.

Software modules/units/blocks configured for execution on computingdevices (e.g., processor 210 as illustrated in FIG. 2-A) may be providedon a computer-readable medium, such as a compact disc, a digital videodisc, a flash drive, a magnetic disc, or any other tangible medium, oras a digital download (and can be originally stored in a compressed orinstallable format that needs installation, decompression, or decryptionprior to execution). Such software code may be stored, partially orfully, on a storage device of the executing computing device, forexecution by the computing device. Software instructions may be embeddedin a firmware, such as an EPROM. It will be further appreciated thathardware modules/units/blocks may be included in connected logiccomponents, such as gates and flip-flops, and/or can be included ofprogrammable units, such as programmable gate arrays or processors. Themodules/units/blocks or computing device functionality described hereinmay be implemented as software modules/units/blocks, but may berepresented in hardware or firmware. In general, themodules/units/blocks described herein refer to logicalmodules/units/blocks that may be combined with othermodules/units/blocks or divided into sub-modules/sub-units/sub-blocksdespite their physical organization or storage. The description may beapplicable to a system, an engine, or a portion thereof.

It will be understood that when a unit, engine, module or block isreferred to as being “on,” “connected to,” or “coupled to,” anotherunit, engine, module, or block, it may be directly on, connected orcoupled to, or communicate with the other unit, engine, module, orblock, or an intervening unit, engine, module, or block may be present,unless the context clearly indicates otherwise. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

These and other features, and characteristics of the present disclosure,as well as the methods of operation and functions of the relatedelements of structure and the combination of parts and economies ofmanufacture, may become more apparent upon consideration of thefollowing description with reference to the accompanying drawings, allof which form a part of this disclosure. It is to be expresslyunderstood, however, that the drawings are for the purpose ofillustration and description only and are not intended to limit thescope of the present disclosure.

FIG. 1-A is a schematic diagram illustrating an exemplary CT systemaccording to some embodiments of the present disclosure. As shown, CTsystem 100 may include a CT scanner 110, a network 120, one or moreterminals 130, a processing engine 140, and a storage 150.

The CT scanner 110 may include a gantry 111, a detector 112, a detectingregion 113, a table 114, and a radiation source 115. The gantry 111 maysupport the detector 112 and the radiation source 115. A subject may beplaced on the table 114 for scanning. The radiation source 115 may emitradiation beams (e.g., X-rays) to the subject. The detector 112 maydetect the radiation beams penetrated through at least part of thesubject within the detection region 113. In some embodiments, the CTscanner 110 may also be part of a multi-modality system including, forexample, PET-CT, SPECT-CT, etc. In some embodiments, a more detailedstructure and mechanism of the CT scanner 110 is illustrated in FIG.1-B. In some embodiments, one or components in the CT system 100 may beomitted. Merely by way of example, the CT system 100 may not include theterminal(s) 130.

The connection between the components in the CT system 100 may bevariable. Merely by way of example, as illustrated in FIG. 1-A, the CTscanner 110 may be connected to the processing engine 140 through thenetwork 120. As another example, the CT scanner 110 may be connected tothe processing engine 140 directly as illustrated by the dotted doublearrow between the CT scanner 110 and the processing engine 140. As afurther example, a terminal 130 may be connected to other portions ofthe system 100 through the network 120. As still a further example, theCT scanner 110 may be connected to a portion of the system 100, e.g.,the processing engine 140 directly as illustrated by the dotted doublearrow between the processing engine 140 and a terminal 130.

For demonstration purposes, a coordinate system as shown in FIG. 1-A maybe used to describe direction related issues in the present disclosure.

The network 120 may include any suitable network that can facilitateexchange of information and/or data for the CT system 100. In someembodiments, one or more components of the CT system 100 (e.g., the CTscanner 110, the terminal 130, the processing engine 140, the storage150) may communicate information and/or data with one or more othercomponents of the CT system 100 via the network 120. For example, theprocessing engine 140 may obtain image data from the CT scanner 110 viathe network 120. As another example, the processing engine 140 mayobtain user instructions from the terminal 130 via the network 120. Thenetwork 120 may be and/or include a public network (e.g., the Internet),a private network (e.g., a local area network (LAN), a wide area network(WAN))), a wired network (e.g., an Ethernet network), a wireless network(e.g., an 802.11 network, a Wi-Fi network), a cellular network (e.g., aLong Term Evolution (LTE) network), a frame relay network, a virtualprivate network (“VPN”), a satellite network, a telephone network,routers, hubs, witches, server computers, and/or any combinationthereof. Merely by way of example, the network 120 may include a cablenetwork, a wireline network, a fiber-optic network, a telecommunicationsnetwork, an intranet, a wireless local area network (WLAN), ametropolitan area network (MAN), a public telephone switched network(PSTN), a Bluetooth™ network, a ZigBee™ network, a near fieldcommunication (NFC) network, or the like, or any combination thereof. Insome embodiments, the network 120 may include one or more network accesspoints. For example, the network 120 may include wired and/or wirelessnetwork access points such as base stations and/or internet exchangepoints through which one or more components of the CT system 100 may beconnected to the network 120 to exchange data and/or information.

The terminal(s) 130 may include a mobile device 131, a tablet computer132, a laptop computer 133, or the like, or any combination thereof. Insome embodiments, the mobile device 131 may include a smart home device,a wearable device, a mobile device, a virtual reality device, anaugmented reality device, or the like, or any combination thereof. Insome embodiments, the smart home device may include a smart lightingdevice, a control device of an intelligent electrical apparatus, a smartmonitoring device, a smart television, a smart video camera, aninterphone, or the like, or any combination thereof. In someembodiments, the wearable device may include a bracelet, a footgear,eyeglasses, a helmet, a watch, clothing, a backpack, a smart accessory,or the like, or any combination thereof. In some embodiments, the mobiledevice may include a mobile phone, a personal digital assistance (PDA),a gaming device, a navigation device, a point of sale (POS) device, alaptop, a tablet computer, a desktop, or the like, or any combinationthereof. In some embodiments, the virtual reality device and/or theaugmented reality device may include a virtual reality helmet, virtualreality glasses, a virtual reality patch, an augmented reality helmet,augmented reality glasses, an augmented reality patch, or the like, orany combination thereof. For example, the virtual reality device and/orthe augmented reality device may include a Google Glass™, an OculusRift™, a Hololens™, a Gear VR™, etc. In some embodiments, theterminal(s) 130 may be part of the processing engine 140.

The processing engine 140 may process data and/or information obtainedfrom the CT scanner 110, the terminal 130, and/or the storage 150. Forexample, the processing engine 140 may generate an image based on datarelating to an object obtained from the CT scanner 110. The datarelating to the object may include projection data corresponding toradiation beams traversing the object. The image may be generated byusing an analytical algorithm, an iterative algorithm, and/or otherreconstruction techniques. In some embodiments, the processing engine140 may include a digital-analog converter (DAC) which may convert theimage data into an analog signal. The analog signal may be processed andtransmitted to the terminal 130 for display.

The processing engine 140 may also determine the focal point or thedisplacement of the focal point of the radiation source 115 of the CTscanner 110. The processing engine 140 may further use the obtainedfocal point or the displacement of the focal point to calibrate the CTscanner 110 or process the image generated based on the data obtainedfrom the CT scanner 110. Detailed descriptions of the processing engine140 are provided elsewhere in the present disclosure (e.g., inconnection with FIG. 3).

In some embodiments, the processing engine 140 may be a computer, a userconsole, a single server or a server group, etc. The server group may becentralized or distributed. In some embodiments, the processing engine140 may be local or remote. For example, the processing engine 140 mayaccess information and/or data stored in the CT scanner 110, theterminal 130, and/or the storage 150 via the network 120. As anotherexample, the processing engine 140 may be directly connected to the CTscanner 110, the terminal 130 and/or the storage 150 to access storedinformation and/or data. In some embodiments, the processing engine 140may be implemented on a cloud platform. Merely by way of example, thecloud platform may include a private cloud, a public cloud, a hybridcloud, a community cloud, a distributed cloud, an inter-cloud, amulti-cloud, or the like, or any combination thereof. In someembodiments, the processing engine 140 may be implemented by a computingdevice 200 having one or more components as illustrated in FIG. 2-A.

The storage 150 may store data, instructions, and/or any otherinformation. In some embodiments, the storage 150 may store dataobtained from the terminal 130 and/or the processing engine 140. In someembodiments, the storage 150 may store data and/or instructions that theprocessing engine 140 may execute or use to perform exemplary methodsdescribed in the present disclosure. In some embodiments, the storage150 may include a mass storage, a removable storage, a volatileread-and-write memory, a read-only memory (ROM), or the like, or anycombination thereof. Exemplary mass storage may include a magnetic disk,an optical disk, a solid-state drive, etc. Exemplary removable storagemay include a flash drive, a floppy disk, an optical disk, a memorycard, a zip disk, a magnetic tape, etc. Exemplary volatileread-and-write memory may include a random access memory (RAM).Exemplary RAM may include a dynamic RAM (DRAM), a double date ratesynchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristorRAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. Exemplary ROM mayinclude a mask ROM (MROM), a programmable ROM (PROM), an erasableprogrammable ROM (EPROM), an electrically erasable programmable ROM(EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM,etc. In some embodiments, the storage 150 may be implemented on a cloudplatform. Merely by way of example, the cloud platform may include aprivate cloud, a public cloud, a hybrid cloud, a community cloud, adistributed cloud, an inter-cloud, a multi-cloud, or the like, or anycombination thereof.

In some embodiments, the storage 150 may be connected to the network 120to communicate with one or more other components in the CT system 100(e.g., the processing engine 140, the terminal 130). One or morecomponents in the CT system 100 may access the data or instructionsstored in the storage 150 via the network 120. In some embodiments, thestorage 150 may be directly connected to or communicate with one or moreother components in the CT system 100 (e.g., the processing engine 140,the terminal 130). In some embodiments, the storage 150 may be part ofthe processing engine 140.

FIG. 1-B is a schematic diagram illustrating an exemplary structure andmechanism of a CT scanner according to some embodiments of the presentdisclosure. FIG. 1-B is a sectional view of the CT scanner 110 along theZ axis or the X axis within the detection region 113. The radiationsource 115 may emit radiation beams 190. The radiation beams 190 maypenetrate an object 180 (e.g., a body, an organ, a tissue, a container)and reach the detector 112. The detector 112 may include a plurality ofdetector units 116 (e.g., detector units 116-1˜116-4). In response tothe incident radiation beams, the plurality of detector units 116 maygenerate signals that may be used for generating an image of the object180. The CT scanner 110 may then transmit the signals to the network120, the processing engine 140, and/or other components of the CT system100.

The radiation source 115 may include a tube, such as a cold cathode iontube, a high vacuum hot cathode tube, a rotating anode tube, etc. Thetube may be powered by a high voltage generator for emitting theradiation beams 190. The radiation beams 190 may be and/or include aparticle ray, a photon ray, or the like, or a combination thereof. Theradiation source 115 may be viewed as a point for approximation. Theradiation beams 190 may also be considered as being emitted from thispoint. The point defined by the radiation source 115 may be referred toas a focal point (e.g., focal point 118). In the present disclosure, theterm “focal point” may also relate to the location of the point.

The radiation beams 190 emitted by the radiation source 115 may include,for example, a plurality of primary radiation beams (e.g., radiationbeam 190-1) and a plurality of scattered radiation beams (e.g.,radiation beam 190-2). The primary radiation beams may propagate along atrajectory path from the focal point 118 to the detector 112. Thetrajectory path may be, for example, a straight connection between thefocal point 118 and the incident point at the corresponding detectorunit 116. The scattered radiation beams may include radiation beamsemitted by the radiation source 115 that are scattered or deflectedwhile penetrating the object 180. The scattered radiation beams maydeviate from their original paths (e.g., trajectory paths). A primaryradiation beam may be one that may contribute to the generation ofdesired imaging data for generating an image of the object 180. Ascattered radiation beam, when detected by a detector unit, may causeartifacts in the image of the object 180.

In some embodiments, for reducing the artifacts in the image of theobject 180, the detector 112 may further include one or moreanti-scatter grids (ASGs, e.g., ASG 117) for limiting the scatteredradiation beams received by the detector units 116. The ASG 117 mayinclude a plurality of plates (e.g., plates 117-1˜117-5). The plates mayinclude materials that can absorb one or more types of radiation. Theradiation absorbing material may include, for example, tungsten, lead,uranium, gold, silver, copper, molybdenum, or the like, or a combinationthereof. The interspaces (or cells) enclosed by the plates may be filledwith air or a radiolucent material. Exemplary radiolucent materials mayinclude, for example, plastic, carbon fiber, aluminum, inorganicnon-metallic material (e.g., paper, ceramic), or the like, or acombination thereof. The ASG 117 may allow the radiation beams passingthrough the cells (e.g., cell 119) defined by the plates to be receivedby the detector units 116 (e.g., detector units 116-1˜116-4). The ASG117 may block (or absorb) at least a majority of the radiation beamshitting the plates of the ASG 117.

The ASG 117 may be installed or placed between the radiation source 115and detector units 116. The plates of the ASG 117 may be aligned towardthe focal point 118 and be distributed along the X direction and/or Zdirection. The primary radiation beams (e.g., radiation beam 190-1)emitted from the focal point 118 may pass through the ASG 117 and bereceived by the detector units 116. The scattered radiation beams (or atleast some of them, e.g., radiation beam 190-2), as deviated from theiroriginal paths, may hit the plates of the ASG 117 and be absorbed by theASG 117. The scattered radiation beams may then be attenuated, orremoved, from the plurality of radiation beams.

In the present disclosure, the X direction and the Z direction, whichare perpendicular to each other, are set parallel with the detector 112or the tangent plane of the center of the detector 112. The X directionand the Z direction are also set parallel with the axis of the detectionregion 113. The Y direction (not shown in FIG. 1-B) is perpendicular toboth the X direction and the Z direction.

In the present disclosure, for the determination of the focal point ofthe radiation source 118, one or more ASGs installed on the CT scanner110 may be non-uniform ASGs. As one aspect, the term “non-uniform ASG”may indicate that the ASG has non-uniformly arranged plates. Forinstance, at least two of the plates of the non-uniform ASG may havedifferent shapes, sizes (e.g., heights), and/or be made of differentmaterials (e.g., with different radiation absorbance), etc. Thenon-uniform ASG of this type may be referred to as Type I non-uniformASG. FIGS. 4-C and 4-D are schematic diagrams illustrating Type Inon-uniform ASGs according to this aspect.

Alternatively or additionally, the term “non-uniform” may indicate thatthe ASG has a structure different from that of a majority of (e.g., morethan 50%) the other ASGs installed on the CT scanner 110. The“non-uniform” ASG itself may have uniformly (e.g., as illustrated inFIG. 4-B) or non-uniformly (e.g., as illustrated in FIGS. 4-C and 4-D)arranged plates. The majority of the other ASGs may share a samestructure. Merely for example, the cells of the majority of the otherASGs may each include one detector unit in one direction (e.g., the Xdirection, the Z direction), while the cells of the non-uniform ASG(s)may each include two or more detector units in the same direction. Thenon-uniform ASG of this type may be referred to as type II non-uniformASG.

In some embodiments, the one or more non-uniform ASGs installed on theCT scanner 110 may only be type I non-uniform ASGs. For instance, allthe ASGs (or the only one ASG) installed on the CT scanner 110 may bethe same type I non-uniform ASGs (e.g., ASGs as illustrated in FIGS. 4-Cand 4-D).

In some embodiments, the one or more non-uniform ASGs installed on theCT scanner 110 may only be type II non-uniform ASGs. The type IInon-uniform ASGs may share a same structure or have differentstructures.

In some embodiments, the one or more non-uniform ASGs installed on theCT scanner 110 may be both the type I and type II non-uniform ASGs.These non-uniform ASGs may share a same structure or have differentstructures.

A detector unit 116 may detect radiation beams penetrating the object180 and then passing through the ASG 117 (if any). The detector unit 116may also be referred to as a detector element or a detector pixel. Thedetector unit 116 may convert the incident radiation beams into asignal. The amplitude of the generated signals may correlate with theintensities of the radiation reaching the detector unit 116. Thedetector unit 116 may include a scintillator and/or a photoelectricsensor, etc. Exemplary materials of the detector unit 116 may include aninert gas (e.g., Xe), CdWO4, Gd2O2S (GOS), or ceramic (e.g., HiLight™),or the like, or a combination thereof.

The detector units 116 may be arranged in a single row or multiple rows.For illustration purposes, FIG. 1-B only illustrates one row. Thedetector units 116 may be arranged on a flat plane (as shown in FIG.1-B) or a curved plane (not shown). In some embodiments, the detectorunits 116 may be aligned with their normal directions pointing at thefocal point 118.

When the ASG(s) is installed on the detector 116, one or more detectorunits may be positioned inside a cell of the ASG. A non-uniform ASG(type I and/or type II) may cover an arbitrary portion of the detector116. Merely for example, the installed non-uniform ASG(s) may cover thewhole detector 116, the central part of the detector 116, and/or theedge part of the detector 116.

It may be noted that, FIG. 1-B is only provided for demonstrationpurposes, and is not intend to apply a limitation to the presentdisclosure. Modification and amendment may be made to FIG. 1-B. Thenumbers, appearances, and relative locations of the components (e.g.,the plates of the ASG 117, the detector units, the radiation beams) ofthe CT scanner 110 are also for illustration and may not reflect theirtrue states in practical use.

FIG. 2-A is a schematic diagram illustrating exemplary hardware and/orsoftware components of an exemplary computing device on which theprocessing engine may be implemented according to some embodiments ofthe present disclosure. As illustrated in FIG. 2-A, the computing device200 may include a processor 210, a storage 220, an input/output (I/O)230, and a communication port 240.

The processor 210 may execute computer instructions (e.g., program code)and perform functions of the processing engine 140 in accordance withtechniques described herein. The computer instructions may include, forexample, routines, programs, objects, components, data structures,procedures, modules, and functions, which perform particular functionsdescribed herein. For example, the processor 210 may be configured toperform the functions relating to the determination of the focal pointor the displacement of the focal point of the radiation source 115 ofthe CT scanner 110.

In some embodiments, the processor 210 may include one or more hardwareprocessors, such as a microcontroller, a microprocessor, a reducedinstruction set computer (RISC), an application specific integratedcircuits (ASICs), an application-specific instruction-set processor(ASIP), a central processing unit (CPU), a graphics processing unit(GPU), a physics processing unit (PPU), a microcontroller unit, adigital signal processor (DSP), a field programmable gate array (FPGA),an advanced RISC machine (ARM), a programmable logic device (PLD), anycircuit or processor capable of executing one or more functions, or thelike, or any combinations thereof.

Merely for illustration, only one processor is described in thecomputing device 200. However, it should be noted that the computingdevice 200 in the present disclosure may also include multipleprocessors, thus steps and/or method steps that are performed by oneprocessor as described in the present disclosure may also be jointly orseparately performed by the multiple processors. For example, if in thepresent disclosure the processor of the computing device 200 executesboth step A and step B, it should be understood that step A and step Bmay also be performed by two or more different processors jointly orseparately in the computing device 200 (e.g., a first processor executesstep A and a second processor executes step B, or the first and secondprocessors jointly execute steps A and B).

The storage 220 may store data/information obtained from the scanner110, the terminal 130, the storage 150, and/or any other component ofthe imaging system 100. In some embodiments, the storage 220 may includea mass storage, a removable storage, a volatile read-and-write memory, aread-only memory (ROM), or the like, or any combination thereof. Forexample, the mass storage may include a magnetic disk, an optical disk,a solid-state drives, etc. The removable storage may include a flashdrive, a floppy disk, an optical disk, a memory card, a zip disk, amagnetic tape, etc. The volatile read-and-write memory may include arandom access memory (RAM). The RAM may include a dynamic RAM (DRAM), adouble date rate synchronous dynamic RAM (DDR SDRAM), a static RAM(SRAM), a thyristor RAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc.The ROM may include a mask ROM (MROM), a programmable ROM (PROM), anerasable programmable ROM (EPROM), an electrically erasable programmableROM (EEPROM), a compact disk ROM (CD-ROM), and a digital versatile diskROM, etc. In some embodiments, the storage 220 may store one or moreprograms and/or instructions to perform exemplary methods described inthe present disclosure. For example, the storage 220 may store a programfor the processing engine 140 for determining a regularization item.

The I/O 230 may input and/or output signals, data, information, etc. Insome embodiments, the I/O 230 may enable a user interaction with theprocessing engine 140. In some embodiments, the I/O 230 may include aninput device and an output device. Examples of the input device mayinclude a keyboard, a mouse, a touch screen, a microphone, or the like,or a combination thereof. Examples of the output device may include adisplay device, a loudspeaker, a printer, a projector, or the like, or acombination thereof. Examples of the display device may include a liquidcrystal display (LCD), a light-emitting diode (LED)-based display, aflat panel display, a curved screen, a television device, a cathode raytube (CRT), a touch screen, or the like, or a combination thereof.

The communication port 240 may be connected to a network (e.g., thenetwork 120) to facilitate data communications. The communication port240 may establish connections between the processing engine 140 and thescanner 110, the terminal 130, and/or the storage 150. The connectionmay be a wired connection, a wireless connection, any othercommunication connection that can enable data transmission and/orreception, and/or any combination of these connections. The wiredconnection may include, for example, an electrical cable, an opticalcable, a telephone wire, or the like, or any combination thereof. Thewireless connection may include, for example, a Bluetooth™ link, aWi-Fi™ link, a WiMax™ link, a WLAN link, a ZigBee link, a mobile networklink (e.g., 3G, 4G, 5G), or the like, or a combination thereof. In someembodiments, the communication port 240 may be and/or include astandardized communication port, such as RS232, RS485, etc. In someembodiments, the communication port 240 may be a specially designedcommunication port. For example, the communication port 240 may bedesigned in accordance with the digital imaging and communications inmedicine (DICOM) protocol.

FIG. 2-B is a schematic diagram illustrating exemplary hardware and/orsoftware components of an exemplary mobile device on which the terminalmay be implemented according to some embodiments of the presentdisclosure. As illustrated in FIG. 2-B, the mobile device 250 mayinclude a communication platform 260, a display 270, a graphicprocessing unit (GPU) 271, a processor 272, an I/O 273, a memory 280,and a storage 275. In some embodiments, any other suitable component,including but not limited to a system bus or a controller (not shown),may also be included in the mobile device 250. In some embodiments, amobile operating system 281 (e.g., iOS™, Android™, Windows Phone™) andone or more applications 282 may be loaded into the memory 280 from thestorage 275 in order to be executed by the processor 272. Theapplications 282 may include a browser or any other suitable mobile appsfor receiving and rendering information relating to the determination ofthe focal point or the displacement of the focal point of the radiationsource 115 of the CT scanner 110 from the processing engine 140. Userinteractions with the information stream may be achieved via the I/O 273and provided to the processing engine 140 and/or other components of theimaging system 100 via the network 120.

To implement various modules, units, and their functionalities describedin the present disclosure, computer hardware platforms may be used asthe hardware platform(s) for one or more of the elements describedherein. A computer with user interface elements may be used to implementa personal computer (PC) or any other type of work station or terminaldevice. A computer may also act as a server if appropriately programmed.

FIG. 3 is a schematic diagram illustrating an exemplary processingengine according to some embodiments of the present disclosure. Theprocessing engine 140 may include an input/output module 310, a scannercontrolling module 320, an image processing module 330, and acalibration module 340. Other modules may also be included in theprocessing engine 140.

The input/output module 310 may be configured to communicate (e.g.,acquire, receive, send) data for the processing engine 140. The data mayinclude data generated by the scanner 110, temporary data generated byprocessing engine 140, control signal generated by the processing engine140 for controlling the scanner 110, instructions for operatingprocessing engine 140 and/or its modules/units, etc. The data may becommunicated with the CT scanner 110, the terminal 130, the network 120,etc.

The scanner controlling module 320 may be configured to generate controlsignal for controlling the CT scanner 110. The control signal may begenerated based on one or more scanning parameters. The scanningparameters may correspond to the type, scanning times, starting time,scanning speed, the scanning region, the scanning condition, etc., ofthe scanning to be performed or being performed by the scanner 110. Thegenerated control signal may be sent to the CT scanner 110 to control orguide the CT scanner 110 for performing a scanning on a subject.

One or more of the scanning parameters may be provided by a user throughthe terminal 130, be acquired from a resource via the network 120, beacquired from a storage device (e.g., the storage 150, the storage 220,the memory 280), or the like, or a combination thereof. One or more ofthe scanning parameters may also be determined by one or moremodules/units of processing engine 140 (e.g., calibration module 340).

The image processing module 330 may be configured to generate (orreconstruct) an image based on the scan date acquired by the scanner110. Different image reconstruction techniques or data processingtechniques may be adopted by the image processing module 330.

In some embodiments, the image processing module 330 may reconstruct oneor more slice images based on the acquired date. A slice image may be a2D cross-sectional image of the scanned subject. The obtained one ormore slice images may be directly used for viewing the inside of thescanned subject. Alternatively or additionally, a plurality of sliceimages may be used for generating a volume image for enhancing thevisual experience. In some embodiments, image processing module 330 maydirectly reconstruct a volume image without generating a plurality ofslice images first during the reconstruction process.

The calibration module 340 may be configured to assess the performanceof one or more devices, modules and/or units of the CT system 100 andobtain one or more performance parameters. For example, the one or moreperformance parameters may relate to the imaging performance of the CTscanner 110. The calibration module 340 may be further configured toadjust (or calibrate) the settings of the one or more devices, modulesand/or units (e.g., the CT scanner 110) of the CT system 100 based onthe obtained performance parameters.

The calibration module 340 may include a focal point determinationsub-module 342. The focal point of the CT scanner 110 may be displaced(e.g., moved, vibrated, oscillated) during its usage (detaileddescription are provided in connection with FIG. 4-A). The focal pointdetermination sub-module 342 may be configured to determine thedisplaced focal point of the radiation source 115. In some embodiments,the focal point determination sub-module 342 may determine thedisplacement of the focal point of the radiation source using anon-uniform ASG (type I and/or type II) according to process 500described in connection with FIG. 5. The displaced focal point (secondfocal point) may be expressed in terms of a coordinate or a displacementalong the X direction and or the Z direction relative to the original(or intended) focal point (first focal point). In the presentdisclosure, unless otherwise noted, “displacement” is a vector whichincludes both the displacement value and the displacement direction.

In some embodiments, during the process 500, a parameter (e.g., a ratioof a first radiation intensity to a second radiation intensity of twodirector units) may be obtained as an intermediate for determining thedisplaced focal point. The calibration module 340 may further include acorrelation determination sub-module 344. The correlation determinationsub-module 344 may be configured to determine the correlation (e.g., inthe form of a lookup table, a function) between the parameter obtainedin process 500 and the focal point. The correlation may then be used todetermine the displaced focal point in process 500.

It may be noted that, the above description about processing engine 140is only for illustration purposes, and is not intended to limit thepresent disclosure. It is understandable that, after learning the majorconcept and the mechanism of the present disclosure, a person ofordinary skill in the art may alter processing engine 140 in anuncreative manner. The alteration may include combining and/or splittingmodules or sub-modules, adding or removing optional modules orsub-modules, etc. All such modifications are within the protection scopeof the present disclosure.

FIG. 4-A is a schematic diagram illustrating the effect of the change ofthe focal point of the radiation source in the CT scanner. Fordemonstration purposes, the effect of the change of the focal point isdescribed with a standard ASG (e.g., ASG 410). In the presentdisclosure, the plates (e.g., plates 410-1˜410-5) of a standard ASG mayhave the same or substantially the same shape, size (including length,width, and height), and made of the same material(s). The cells definedby the plates of the standard ASG may also have the same orsubstantially the same shape and/or size. Cells (e.g., cell 411) of thestandard ASG may each include only one detector unit (e.g., detectorunits 412-1˜412-4). The plates of the standard ASG 410 are alignedtoward a first focal point (the original or intended focal point, e.g.,focal point 415) of the radiation source 115. Standard ASGs have beenwidely adopted in the prior art.

During the usage of the CT scanner 110, the focal point of the radiationsource 115 may be displaced (e.g., moved, vibrated, oscillated) due tovarious factors. The various factors may include, for example, thethermal expansion and/or contraction of the radiation source 115 duringthe emitting of radiation beams, the gravity, the centrifugal force, thevibration of the radiation source 115 caused by the running of CTscanner 110, the aging of the mechanical structure(s) of CT scanner 110,the imaging technique adopted by the CT scanner 110 (e.g., z-flyingfocal spot technology), or the like, or a combination thereof. Adeviation of the focal point of the radiation source 115 from itsintended position may be expressed in terms of one or more deviationcomponent(s) along the X, Y and/or Z direction. In some embodiments, thedeviation component along the Y direction may show a negligibleinfluence and may be omitted.

At a certain time point, the radiation source 155 may have a secondfocal point (e.g., focal point 416). As the plates of ASG 410 arealigned toward the focal point 415, some primary radiation beams (e.g.,radiation beam 419) may still find their way passing through the ASG 410to the detector units (e.g., detector units 412-2), while some of theprimary radiation beams (e.g., radiation beam 418) may be blocked by theplates (e.g., plate 410-2) of the ASG 410. As a result, a part (e.g.,part 413-1) of each of at least some detector units may receive fewerradiation beams compared to the other part (e.g., part 413-2), and ashadow may form (e.g., shadow 414-1˜414-4). The existence of shadows maycause a reduction of the intensity of radiation received by a detectorunit, which may in turn result in a reduction of the quality of an imagegenerated therefrom (e.g., in the form of artifacts or reducedresolution).

When the standard ASG 410 is used, after the change or displacement ofthe focal point, the reductions of the radiation intensities occurred onall the detector units may be to the same or similar degree.

The reduction of the image quality caused by shadows may be compensated(e.g., by the calibration module 340 and/or the Image processing module330) using various hardware related (e.g., focus point tracing) orsoftware related (e.g., image post-processing) techniques. Thesetechniques may involve the determination of the displaced focal point(e.g., the location of a displace focal point (or referred to as asecond focal point) relative to the original or intended focal point (orreferred to as the first focal point)). Theoretically, the second focalpoint may be determined based on the reduction of the radiationintensity detected by one (or more for eliminating errors) of thedetector units. However, besides the change of the focal point, one ormore other factors (e.g., mA modulation, kV ripple, mA ripple, filamentestablishment) may also cause the reduction of the radiation intensityupon all the detector units. With a standard ASG, it is difficult todifferentiate the portion of the reduction of the radiation intensitycaused by the displacement of the focal point from the portion of thereduction caused by the one or more other factors.

In the present disclosure, the CT scanner 110 may be equipped with anon-uniform ASG for identifying the reduction of the radiation intensitycaused by the displacement of the focal point. In some embodiments, thefocal point determination sub-module 342 may determine the displacedfocal point using the non-uniform ASG according to process 500descripted in connection with FIG. 5. The non-uniformity may beeffectuated by the arrangements of the plates of an ASG, the sizes ofthe plates, the materials of the plates, or the like, or a combinationthereof. For instance, in a non-uniform ASG, cells formed by the platesenclose different numbers of detector units. As another example, anon-uniform ASG may be formed by plates of different shapes or sizes(e.g., different heights). FIGS. 4-B, 4-C, and 4-D illustrate exemplarynon-uniform ASGs according to some embodiments of the presentdisclosure. It may be noted that, FIGS. 4-B, 4-C, and 4-D are onlyprovided for demonstration purposes and not intend to limit the scope ofthe present disclosure. The illustrated non-uniform ASGs arenonexclusive and may have different forms when applied in practical use.

FIG. 4-B illustrates an exemplary non-uniform ASG according to someembodiments of the present disclosure. ASG 420 may be installed as atype II non-uniform ASG. ASG 420 may be equipped on the CT scanner 110for facilitating the determination of a displaced or second focal point426 relative to an intended or first focal point 425 according to, forexample, process 500 described in connection with FIG. 5. The plates(e.g., plates 420-1˜420-3) of the ASG 420 may also have the same orsubstantially the same shape, size, and be made of the same material(s).The cells defined by the plates of the ASG 420 may also have the same orsubstantially the same configuration (e.g., shape and size).Distinguished from a standard ASG (e.g., ASG 410), a cell (e.g., cell421) of ASG 420 may include more than one detector units (e.g., detectorunits 422-1˜422-4) along at least one direction (e.g., X direction, Zdirection, or both). For instance, each cell of ASG 420 may include twodetector units (four in total) along both the X direction and the Zdirection.

The plates of ASG 420 may be aligned toward the first focal point 425(the original or intended focal point) of the radiation source 115. Whenthe focal point of the radiation source 115 changes from the first focalpoint 425 to the second focal point 426, some detector units (firstdetector units, e.g., detector units 422-1-And 422-3) may be covered bythe shadows (e.g., shadows 424-1 and 424-2) caused by the displacementof the focal point, while some detector units (second detector units,e.g., detector unit 422-2 and 422-4) may be free of the shadows causedby the same reason. As used herein, a first detector unit may refer to adetector unit that receives or detects a different amount of radiationwhen the focal point of the radiation source is displaced compared towhen the focal point of the radiation source is at its original orintended location, assuming that the radiation source emits the sameamount of radiation beams regardless of the location of its focal point.As used herein, a second detector unit may refer to a detector unit thatreceives the same (or substantially the same) amount radiation when thefocal point of the radiation source is displaced from its original orintended location, assuming that the radiation source emits the sameamount of radiation beams regardless of the location of its focal point.The reductions of the radiation intensities caused by the change of thefocal point detected by the first detector units may be different fromthe one detected by the second detector units. The difference may beused (e.g., by the focal point determination sub-module 342) fordetermining the second focal point 426.

It may be noted that, the first detector units and the second detectorunits may exchange their roles as a first detector unit at leastpartially covered by shadow or a second detector unit free of shadowwhen the focal point is displaced along the direction opposite to thatillustrated in FIG. 4-B. For example, the second detector units 422-2and 422-4 may be covered by shadows caused by the displacement of thefocal point, while the first detector units 422-1 and 422-3 may be freeof shadows caused by the same reason. However, the difference betweenthe radiation intensities of the first detector units and the seconddetector units may still be used for determining the second focal point426.

The radiation intensities of a first-second detector unit pair (e.g.,the detector units 422-1 and 422-2, the detector units 422-2 and 422-3,or the detector units 422-1 and 422-4) may be used for determining thesecond focal point 426. In some embodiments, the radiation intensitiesof at least one arbitrary or predetermined pair of adjacent firstdetector unit and second detector unit (e.g., the detector units 422-2and 422-3) may be used for determining the second focal point 426.

FIG. 4-C illustrates an exemplary non-uniform ASG according to someembodiments of the present disclosure. ASG 430 may be equipped on the CTscanner 110 for facilitating the determination of a displaced or secondfocal point 436 relative to an intended or first focal point 435according to, for example, process 500 described in connection with FIG.5. The plates (e.g., plates 440-1˜440-5) of the ASG 430 may still havesame or substantially same shapes, sizes, and the materials. The cellsof ASG 430, however, may not be uniformly configured. One or more cells(the irregular cells, e.g., cell 431-1) of ASG 430 may include more thanone detector units (e.g., detector units 432-1 and 432-2 as illustratedin FIG. 4-C) along at least one direction (e.g., the X direction, the Zdirection, or both). For instance, ASG 430 may have one or moreirregular cells including two detector units (two in total) along Xdirection and one or more irregular cells including two detector units(two in total) along Z direction. As another example, ASG 430 may haveone or more irregular cells including two detector units (four in total)along both the X direction and the Z direction. The plates of ASG 430may be aligned toward the first focal point 435 (the original orintended focal point) of the radiation source 115. As used herein, aregular cell may refer to one that encloses one detector unit (e.g.,cells 431-2 and 431-3 as illustrated in FIG. 4-C). As used herein, anirregular cell may refer to one that encloses more than one detectorunit (e.g., the cell 431-1 as illustrated in FIG. 4-C).

In the ASG 430, only a detector unit (e.g., detector units 432-1 and432-2) enclosed within an irregular cell may be designated as a firstdetector unit that is at least partially covered by the shadow or asecond detector unit that is free of the shadow occurred when the focalpoint of the radiation source is displaced. Other detector units (e.g.,detector units 432-3 and 432-4) enclosed in regular cells may always becovered by shadows (e.g., shadows 434-2 and 434-3) when the focal pointis displaced regardless of the direction of the displacement, and arenot included in determining the focal point.

When the focal point of the radiation source 115 is displaced from thefirst focal point 435 to the second focal point 436, a first detectorunit (e.g., the detector unit 432-1) within an irregular cell may becovered by the shadow (e.g., shadow 434-1) caused by displacement of thefocal point, while a second detector unit (e.g., detector unit 432-2)within a same irregular cell or different irregular cells may be free ofthe shadows caused by the same reason. The difference between theradiation intensities received by the first detector unit and the seconddetector unit may be used (e.g., by the focal point determinationsub-module 342) for determining the second focal point 436. It may alsobe noted that, the first detector unit(s) and the second detectorunit(s) may exchange their roles when the focal point is displaced alongthe along the direction opposite to that illustrated in FIG. 4-C.

In some embodiments, the radiation intensities of a first detector unitand a second detector unit within an arbitrary or predeterminedirregular cell may be used (e.g., by focal point determinationsub-module 342) for determining the second focal point 436. The firstdetector unit and the second detector unit may be adjacent to oneanother.

FIG. 4-D illustrates an exemplary non-uniform ASG according to someembodiments of the present disclosure. ASG 440 may be equipped on the CTscanner 110 for facilitating the determination of a displaced or secondfocal point 446 relative to an intended or first focal point 445according to, for example, process 500 described in connection with FIG.5. One or more plates (the abnormal plates, e.g., plates 440-2) may havedifferent shapes and/or sizes compared to other plates (e.g., plates440-1, 440-2, 440-3 and 430-4) of the ASG 440. Each cell of the ASG 440may enclose one detector unit (e.g., detector units 442-1˜442-4). A cell(e.g., cells 441-1 and 441-2 as illustrated in FIG. 4-D) surrounded byone or more (along either or both of the X direction and the Zdirection) abnormal plates may be referred to as an abnormal cell. Oneabnormal plate may define a pair of abnormal cells. For instance, theASG 440 may include one or more pairs of abnormal cells with one or moreabnormal plates along either or both of the X direction and the Zdirection. The plates of ASG 430 may be aligned toward the first focalpoint 435 (the original or intended focal point) of the radiation source115. As used herein, a regular cell may refer to one that encloses onedetector unit (e.g., the cell enclosing detector unit 432-3 and the cellenclosing 432-4 as illustrated in FIG. 4-D.). As used herein, normalplates may refer to the majority of plates included in an ASG which mayshare a same size (e.g., height). An abnormal plate may refer to onethat has a different size compared to the normal plates (e.g., the plate440-2 as illustrated in FIG. 4-D). An abnormal cell may refer to onethat surrounded by one or more abnormal plates (e.g., the cells 441-1and 441-2 as illustrated in FIG. 4-D).

In the ASG 440, only a detector unit (e.g., detector units 442-1 and442-2) enclosed within an abnormal cell may be designated as a firstdetector unit that is at least partially covered by the shadow or asecond detector unit that is free of the shadow occurred when the focalpoint of the radiation source is displaced. Other detector units (e.g.,detector units 442-3 and 442-4) may always be covered by shadows (e.g.,shadows 444-2 and 444-3) when the focal point is displaced regardless ofthe direction of the displacement, and are not included in determiningthe focal point.

When the focal point of the radiation source 115 is displaced from thefirst focal point 445 to the second focal point 446, a first detectorunit (e.g., the detector unit 444-1) within an abnormal cell may have alarger part covered by the shadow (e.g., shadow 444-1) caused by thedisplacement of the focal point, while a second detector unit (e.g.,detector unit 442-2) within another abnormal cell (e.g., an adjacent onewhich shares a same abnormal plate) may have a smaller part covered bythe shadow caused by the same reason. The difference between theradiation intensities received by the first detector unit and the seconddetector unit may be used (e.g., by the focal point determinationsub-module 342) for determining the second focal point 446. It may alsobe noted that, the first detector unit(s) and the second detectorunit(s) may exchange their roles when the focal point is displaced alongthe direction opposite to that illustrated in FIG. 4-D.

In some embodiments, the radiation intensities of a first detector unitand a second detector unit within an arbitrary or predetermined pair ofabnormal cells may be used (e.g., by focal point determinationsub-module 342) for determining the second focal point 446. The firstdetector unit and the second detector unit may be adjacent to oneanother.

It may be noted that, the non-uniform ASG illustrated in FIG. 4-B, FIG.4-C, and FIG. 4-D are provided only for demonstration purposes, and arenot intended to be limiting. Numerous modification may be made to theASG 410, 420, or 430. For example, the cells of ASG 410, the irregularcell(s) of ASG 420, or the abnormal cell(s) of ASG 430 may include moredetector units along either or both of the X direction and the Zdirection.

In some embodiments, ASG 410 may also be made as a non-uniform ASG byusing different material with different radiation blocking (orabsorbing) properties for different plates. For example, one or more ofthe plates of ASG 410 (e.g., the plate 410-2) may have smaller radiationblocking capacities compared to other plates. When the focal point ofradiation 115 is displaced from the first focal point 415 to the secondfocal point 416. The shadow region of detector 412-2 may receive moreradiation than other shadow regions. When the focal point of radiation115 is displaced along the direction opposite to that illustrated inFIG. 4-A, the shadow region of detector 412-1 may receive more radiationthan other shadow regions. The detector unit 412-1 may be assigned asthe first detector unit receiving reduced radiation, and the detectorunit 412-2 may be assigned as the second detector unit receiving thesame amount of radiation when the focal point is displaced compared towhen the focal point is located at its original or intended position.

FIG. 5 is a schematic diagram illustrating an exemplary process fordetermining the focal point of the radiation source according to someembodiments of the present disclosure. Process 500 may be performed bythe focal point determination sub-module 342 for determining the focalpoint of a radiation source belonging to a CT scanner 110 equipped withone or more non-uniform ASG (type I and/or type II). The CT scanner 110may include only the non-uniform ASG, or include both the standard ASGand the non-uniform ASG. In some embodiments, one or more operations ofprocess 500 illustrated in FIG. 5 for determining the focal point of theradiation source may be implemented in the CT system 100 illustrated inFIG. 1. For example, the process 500 illustrated in FIG. 5 may be storedin the storage 150 in the form of instructions, and invoked and/orexecuted by the processing engine 140 (e.g., the processor 210 of thecomputing device 200 as illustrated in FIG. 2-A).

The focal point determination sub-module 342 may determine adisplacement of the focal point from a first focal point to a secondfocal point via process 500 along the X direction or the Z direction.The displacement may then be used to generate the coordinate of thesecond focal point, or be directly used (e.g., by the calibration module340 and/or the Image processing module 330) for compensating thereduction of the image quality caused by the change of focal point viaone or more hardware related (e.g., focus point tracing) and/or software(e.g., image post-processing) related techniques. In some embodiments, acalibration instruction for calibrating the CT scanner 110 may begenerated by the calibration module 340 and/or the scanner controllingmodule 320 and sent to the CT scanner for calibration.

In 510, the focal point determination sub-module 342 may determine afirst intensity of first radiation incident on a first detector unit ofthe CT scanner 110. In 520, the focal point determination sub-module 342may determine a second intensity of second radiation incident on asecond detector unit of the CT scanner 110. The first radiation and thesecond radiation may be emitted from the radiation source 115 with thesecond focal point. The first radiation and the second radiation may beemitted at a same time point or within a same time interval.

The CT scanner 110 may include a non-uniform ASG as described inconnection with FIGS. 4-B to 4-D. The first detector unit and the seconddetector unit may be determined by a user, by the focal pointdetermination sub-module 342, or the like, or a combination thereof. Thefirst detector unit and the second detector unit may be determined basedon the structure of the non-uniform ASG (see the descriptions of FIGS.4-B to 4-D). In some embodiments, the first detector unit and the seconddetector unit adjacent to one another may be determined. In someembodiments, the first detector unit and the second detector unit spacedapart may be determined.

In some embodiments, the ASG 420 may be the non-uniform ASG installed onthe CT scanner 110. The first detector unit and the second detector unitmay be included in the same cell. For example, the detector units 422-1and 422-2 may be determined as the first detector unit and the seconddetector units. Alternatively or additionally, the first detector unitand the second detector unit may be included in different cells. Thedifferent cells may be adjacent to one another or spaced apart. Forexample, the detector units 422-2 and 422-3 (or the detector units 422-1and 422-4) may be determined as the first detector unit and the seconddetector units.

In some embodiments, the ASG 430 may be the non-uniform ASG installed onthe CT scanner 110. The first detector unit and the second detector unitmay be included in the same cell. For example, the detector units 432-1and 432-2 may be determined as the first detector unit and the seconddetector units. Alternatively or additionally, the first detector unitand the second detector unit may be included in different cells sharinga same (or substantially same) structure. The different cells may beadjacent to one another or spaced apart.

In some embodiments, the ASG 440 may be the non-uniform ASG installed onthe CT scanner 110. The non-uniform ASG 440 may include abnormal cells(e.g., cells 441-1 and 441-2). The abnormal cells may include plates ofdifferent heights. The first detector unit and the second detector unitmay be included in different abnormal cells having different structures.The different abnormal cells may be adjacent to one another or be spacedapart. For example, the detector units 442-1 and 442-2 may be determinedas the first detector unit and the second detector unit.

The focal point determination sub-module 342 may determine the firstintensity and the second intensity based on the signals generated by thefirst detector unit and the second detector unit in response to thefirst radiation and the second radiation, respectively. For example, thefirst intensity and the second intensity may correspond to theamplitudes, average amplitudes, or integrals of the amplitudes of thecorresponding signals over a predetermined time interval. Due to theconfiguration of the non-uniform ASG, after the displacement of thefocal point, the first intensity and the second intensity may becomedifferent.

The focal point determination sub-module 342 may determine the firstintensity and the second intensity in real time, or based on the scandata (including the information relating to the signals generated by thefirst detector unit and the second detector unit) stored in a storagedevice (e.g., storage 150, storage 220, storage 275, memory 280) at alater time. Due to the equivalence of 510 and 520, the two operationsmay be performed in any sequence or be performed simultaneously.

In 530, the focal point determination sub-module 342 may determine thedisplacement of the focal point based on the first intensity and thesecond intensity. The direction (e.g., the X direction, the Z direction)along which the first detector unit and the second detector unit arelocated may define the direction of the displacement determined. Forexample, to determine the displacement of the focal point along both theX direction and the Z direction, a first pair of a first detector unitand a second detector unit located along the X direction and a secondpair of a first detector unit and a second detector unit located alongthe Z direction may be selected. Process 500 may then be performed twicefor obtaining the displacements along both directions.

In some embodiment, the focal point determination sub-module 342 maydetermine the displacement of the focal point based at least in part onat least one parameter relating to the configuration of the ASG. Forinstance, the at least one parameter may include a height of at leastsome plates of the ASG and a distance from the second focal point to atop of the at least a portion of the ASG. An exemplary process aredescribed in connection with FIGS. 6, 7-A, and 7-B.

Merely by way of example, the focal point determination sub-module 342may determine the displacement of the focal point based on a ratio ofthe first intensity detected by the first detection unit to the secondintensity detected by the second detection unit. In some embodiments,the focal point determination sub-module 342 may obtain a correlationbetween the displacement and the ratio, then determine the displacementbased on the ratio and the correlation. An exemplary process aredescribed in connection with FIGS. 8 and 9.

In some embodiments, a plurality of pairs of first and second detectorunits may be used for determining the displacement of the focal pointalong one direction. The focal point determination sub-module 342 mayperform process 500 upon each of the plurality of detector unit pairs togenerate a plurality of results, and determine the displacement alongthat direction based on the plurality of results. Alternatively, thefocal point determination sub-module 342 may determine the firstradiation intensity and second radiation intensity based on (e.g., mean,integral) the signals generated by the first detector units and thesecond detector units, respectively.

Process 500 may be performed prior to or during the scanning of asubject using CT scanner 100. The subject may be a phantom, or a testobject (e.g., patient). Signals detected by the detector units (e.g.,the first detector unit and the second detector unit) used fordetermining the focal point may be included in, or excluded from, thedata used for generating an image of the subject.

It may be noted that the above descriptions of the determining of thefocal point are only for demonstration purposes, and not intended tolimit the scope of the present disclosure. It is understandable that,after learning the major concept and the mechanism of the presentdisclosure, a person of ordinary skill in the art may alter process 500in an uncreative manner. For example, the operations above may beimplemented in an order different from that illustrated in FIG. 5. Oneor more optional operations may be added to the flowcharts. One or moreoperations may be divided or be combined. All such modifications arewithin the protection scope of the present disclosure.

FIG. 6 is a schematic diagram illustrating an exemplary process fordetermining the displacement of the focal point based on the firstintensity and the second intensity according to some embodiments of thepresent disclosure. Process 600 may be performed to achieve 530 ofprocess 500. In some embodiments, process 600 may be performed by thefocal point determination sub-module 342. In some embodiments, one ormore operations of process 600 illustrated in FIG. 6 for determining thefocal point of the radiation source may be implemented in the CT system100 illustrated in FIG. 1. For example, the process 600 illustrated inFIG. 6 may be stored in the storage 150 in the form of instructions, andinvoked and/or executed by the processing engine 140 (e.g., theprocessor 210 of the computing device 200 as illustrated in FIG. 2).

In 610, the focal point determination sub-module 342 may obtain areference radiation intensity for at least one of the first detectorunit and the second detector unit. The reference radiation intensity maycorrespond to the intensity of the radiation received by the firstdetector unit or the second detector when the focal point of theradiation source 115 is at (approximately or precisely) the first focalpoint. As used herein, “approximately” may indicate that the deviationfrom the first focal point (the original or intended focal point) islower than a threshold. In some embodiments, the threshold may be, e.g.,1 micron, 2 microns, 5 microns, 10 microns, 20 microns, 50 microns, 100microns, etc. In some embodiments, the threshold may be, 1%, 2%, 3%, 4%,5%, 6%, 8%, 10%, etc., of the range within which the radiation source isallowed to move. The reference radiation intensity may be determinedprior to or during the scanning of a subject using CT scanner 100. Forexample, the reference radiation intensity may be retrieved from astorage device (e.g., storage 150, storage 220, storage 275, memory280), determined based on one of the system parameters provided with theCT scanner 100. As another example, the reference radiation intensitymay be obtained based on one or more signals generated by one or moredetector units of the CT scanner 100.

In some embodiments, the reference radiation intensity may be obtainedby the following process. The scanner control module 320 may send acontrol signal to the CT scanner 110. The CT scanner 110 may respond tothe control signal, and cause the radiation source 115 to emitradiation. During the radiation emission process, the temperature of theradiation source 115 may rise (e.g., by running the radiation source 115originally at a sleep mode or a low-load mode), or drop (e.g., bycooling the radiation source 115 originally at an operative mode or ahigh-load mode). The focal point of the radiation source 115 may bedisplaced due to thermal expansion or contraction accordingly.

The signals generated by the first detector unit and the second detectorunit may be extensively collected (e.g., 1˜500 samples per second)during the radiation emission process. A plurality of first intensitiesand second intensities may be obtained. When the sum of the firstintensity and the second intensity collected at a time point (time pointA) reaches its maximum compared to other time points, the focal point ofthe radiation source 115 at the time point A may be considered as theone (the first focal point) toward which the plates of the ASG arealigned. In some embodiments, the first intensity and the secondintensity collected at the time point A may be selected (e.g., by a useror by the focal point determination sub-module 342) as referenceradiation intensities for the first detector unit and the seconddetector unit, respectively. In some embodiments, the average value(weighted or not weighted) of the first intensity and the secondintensity of the time point A may be determined (e.g., by a user or bythe focal point determination sub-module 342) as one reference radiationintensity for both the first detector unit and the second detector unit.

In some embodiments, a plurality of pairs of first and second detectorunits may be used for determining the displacement of the focal pointalong one direction. The focal point determination sub-module 342 mayobtain one or more reference radiation intensities for each of theplurality of detector unit pairs. Alternatively, the focal pointdetermination sub-module 342 may determine a common reference radiationintensity set (including one or more reference radiation intensities)for the plurality of detector unit pairs.

The obtained one or more reference radiation intensities may then bestored in a storage device (e.g., storage 150, storage 220, storage 275,memory 280) When the focal point determination sub-module 342 is todetermine the displacement of the focal point through process 600, thefocal point determination sub-module 342 may obtain at least one of thereference radiation intensities.

In 620, the focal point determination sub-module 342 may obtain at leastone ASG parameter relating to the configuration of the non-uniform ASG.The ASG parameter may relate to the height of at least a portion of theASG, the distance form the second focal point to a top of the at least aportion of the ASG, the length and/or the width of one or more cells ofthe ASG, or the like, or a combination (e.g., a calculation) thereof.The ASG parameter may be retrieved from a storage device (e.g., storage150, storage 220, storage 275, memory 280), determined based on one ofthe system parameters provided with the non-uniform ASG, or measured bya user of the ASG or the CT scanner 110, or a combination thereof.

In 630, the focal point determination sub-module 342 may determine thedisplacement of the focal point based on the at least one referenceradiation intensity obtained in 610, the at least one ASG parametersobtained in 620, the first intensity obtained in 510, and the secondintensity obtained 520. The direction (e.g., the X direction, the Zdirection) along which the first detector unit and the second detectorunit are located may define the direction of the displacement determinedin 630.

In some embodiments, the focal point determination sub-module 342 mayperform the process 600 according to the description of FIGS. 7-A and7-B.

FIGS. 7-A and 7-B are schematic diagrams of the process illustrated inFIG. 6 according to some embodiments of the present disclosure. It maybe noted that, for demonstration purposes, FIGS. 7-A and 7-B onlyillustrate the process 600 with the non-uniform ASG 420 as illustratedin FIG. 4-B. However, other non-uniform ASGs (e.g., ASGs 430 and 440illustrated in FIGS. 4-C and 4-D) descripted or implied in the presentdisclosure may also be used for the process 600 with a similar manner.

The plates (e.g., the plates 420-1, 420-2, and 420-3) of the ASG 420 arealigned toward a focal point 710 (first focal point). During theoperation of the CT scanner 110, the focal point of the radiation source115 may be displaced along the X direction or the Z direction (parallelto the detector units). For example, the focal point may be displacedtoward one direction to the focal point 712 (as shown in FIG. 7-A), ortoward the opposite direction to the focal point 714 (as shown in FIG.7-B). The focal point being at focal point 712 may cause shadows 724-1and 724-2 on the first director units 422-1 and 422-3. The focal pointbeing at focal point 714 may cause shadows 724-3 and 724-4 on the firstdirector units 422-2 and 422-4.

For the ASG 420, any pair of adjacent detector units including a firstdetector unit and a second detector unit may be identified (e.g., by auser or by the focal point determination sub-module 342). In FIGS. 7-Aand 7-B, detector unit 422-2 and 422-3 are determined as the firstdetector unit and the second detector unit, respectively.

The focal point determination sub-module 342 may determine the directionof the displacement by comparing the changes of the radiationintensities occurred on the detector units 422-2 and 422-3. For example,when the detector unit 422-3 has a larger reduction of the radiationintensity (e.g., caused by shadow 724-2), the focal point determinationsub-module 342 may determine that the displacement has occurred in apattern as shown in FIG. 7-A. When the detector unit 422-2 has a largerreduction of the radiation intensity, the focal point determinationsub-module 342 may determine the displacement has occurred in a patternas shown in FIG. 7-B.

In some embodiments, the focal point determination sub-module 342 maydirectly compare the radiation intensities of the detector units 422-2and 422-3 for determining the direction of the displacement. The onewith a smaller intensity may be determined as the one having a largerreduction of the radiation intensity.

In some embodiments, the focal point determination sub-module 342 mayfirst determine the reductions of the radiation intensities occurred oneach of the detector units 422-2 and 422-3 with the correspondingreference radiation intensities obtained in 610. For example, the focalpoint determination sub-module 342 may obtain a ratio of the currentlyreceived radiation intensity to the corresponding reference radiationintensity for each of the detector units 422-2 and 422-3. The one with asmaller ratio may be determined as the one having a larger reduction ofthe radiation intensity.

In some embodiments, when the displacement is determined to haveoccurred in a pattern as shown in FIG. 7-A, the focal pointdetermination sub-module 342 may determine the displacement according toEquation (1) in 630 of process 600, which may be expressed as:

$\begin{matrix}{{D_{1} = {\left( {1 - \frac{I_{2}}{I_{R2}}} \right)\;\frac{L_{2}H_{F2A}}{H_{ASG}}}},} & (1)\end{matrix}$

where D₁ is the value of the displacement in a pattern as shown in FIG.7-A, I₂ is the intensity (second intensity) of the radiation received bythe detector unit 422-3 (second detector unit), I_(R2) is the referenceradiation intensity for the detector unit 422-3, L₂ is the length of thedetector unit 422-3 in the X direction or the Z direction, H_(ASG) isthe height of the plate (e.g., plate 420-2) of the ASG 420 shared by thedetector units 422-2 and 422-3, and H_(F2A) is the distance from thesecond focal point to the top of the shared plate in a directionperpendicular to the detector 422-2 and/or 422-3 (e.g., the Ydirection). As the displacement along the Y direction is omitted,H_(F2A) may be considered as the distance from the first focal point tothe top of the shared plate in the Y direction.

In some embodiments, when the displacement is determined to haveoccurred in a pattern as shown in FIG. 7-B, the focal pointdetermination sub-module 342 may determine the displacement according toEquation (2) in 630 of process 600, which may be expressed as:

$\begin{matrix}{{D_{2} = {\left( {1 - \frac{I_{1}}{I_{R1}}} \right)\;\frac{L_{1}H_{F2A}}{H_{ASG}}}},} & (2)\end{matrix}$

where D₂ is the value of the displacement in a pattern as shown in FIG.7-B, I₁ is the intensity (first intensity) of the radiation received bythe detector unit 422-2 (first detector unit), I_(R1) is the referenceradiation intensity for the detector unit 422-2, L₁ is the length of thedetector unit 422-2 in the X direction or the Z direction, and H_(ASG)and H_(F2A) hold the same meaning as in Equation (1).

H_(ASG) and H_(F2A) may be obtained as ASG parameters in 620 of process600. H_(ASG) and H_(F2A) may be provided with CT scanner 110 or ASG 420as system parameters, or be measured directly by a user.

L₁ and L₂ may have a same value or different values. In someembodiments, L₁ and L₂ may be provided with CT scanner 110 as systemparameters or be measure form the CT scanner 110 by a user. In someembodiments, L₁ and L₂ may be obtained as or determined based on the ASGparameters in 620 of process 600. For example, L₁ and L₂ may beconsidered as half of the length of the cells defined by the plates420-1, 420-2, and 420-3 in the X direction or the Z direction.

In some embodiments, L₁ and L₂ may both have a same value L. A parameterwith a value of LH_(F2A)/H_(ASG) may be provided with CT scanner 110 orASG 420, and be obtained as part of the ASG parameter in 620 of process600.

I_(R1) and/or I_(R2) may be obtained in 610 of process 600. In someembodiments, both of I_(R1) and I_(R2) may be obtained in 610. Forexample, I_(R1) and I_(R2) may be used to determine the pattern of thedisplacement. In some embodiments, the pattern of the displacement maybe determined without using I_(R1) or I_(R2) (e.g., by directlycomparing the radiation intensities of the detector units 422-2 and422-3), and one of I_(R1) or I_(R2) may be obtained in 610 according tothe determined pattern. In some embodiments, I_(R1) and/or I_(R2) may bereplaced by the radiation intensity of the detector unit free of shadowcaused by the displacement of the focal point. For example, to determineD₁, I₁ may be used to replace I_(R2) in Equation (1); to determine D₂,I₂ may be used to replace I_(R1) in Equation (2).

FIG. 8 is a schematic diagram illustrating an exemplary process fordetermining the displacement of the focal point based on the firstintensity and the second intensity according to some embodiments of thepresent disclosure. Process 800 may be performed to achieve 530 ofprocess 500. Process 800 may be performed by the focal pointdetermination sub-module 342. In some embodiments, one or moreoperations of process 800 illustrated in FIG. 8 for determining thefocal point of the radiation source may be implemented in the CT system100 illustrated in FIG. 1. For example, the process 800 illustrated inFIG. 8 may be stored in the storage 150 in the form of instructions, andinvoked and/or executed by the processing engine 140 (e.g., theprocessor 210 of the computing device 200 as illustrated in FIG. 2).

In 810, the focal point determination sub-module 342 may determine aratio of the first intensity to the second intensity. Then in 820, thefocal point determination sub-module 342 may obtain a correlationbetween the ratio and the displacement of the focal point. Thecorrelation may be, for example, a mathematical function (e.g., apolynomial, a piecewise function), or a lookup table (the items of whichmay each include a ratio and a corresponding displacement), etc. In 830,the focal point determination sub-module 342 may determine thedisplacement of the focal point based on the ratio and the correlation.For example, the displacement may be obtained by inputting the ratiointo the mathematical function, or by searching the item with the same(precisely or approximately) ratio in the lookup table. In someembodiments, an interpolation or extrapolation may be performed todetermine a displacement based on the values available in the lookuptable.

The correlation between the ratio and the displacement of the focalpoint may be generated by the correlation determination sub-module 344.An exemplary technique for generating the correlation is discussed inconnection with FIG. 9.

FIGS. 9-A and 9-B are schematic diagrams illustrating exemplarytechniques for generating the correlation between the ratio of the firstintensity to the second intensity and the displacement of the focalpoint according to some embodiments of the present disclosure. Detector950 may be the same as or similar to the detector 112. Detector 950 mayinclude a plurality of detector units and one or more non-uniform ASGs(not shown in FIG. 9 for simplicity). The one or more non-uniform ASGsmay be configured according to a focal point 901 (first focal point) ofthe radiation source 115. A plate 910 made of radiation absorbingmaterial may be placed between the radiation source 115 and the detector950 for determining the correlation. The plate 910 may have a pinhole915 through which a portion of the radiation emitted by the radiationsource 115 may pass and reach the detector 950. A line 960 linking thecenter point of the pinhole 915 and the focal point 901 may coincidewith or parallel to (approximately or precisely) the Y direction. Whenthe focal point of the radiation source 115 is at the focal point 901, aregion R₁ of detector 950 may be illuminated by the radiation emittedfrom the radiation source 115.

To determine the correlation between the ratio of the first intensity(detected by a first detector unit) to the second intensity (detected bya first detector unit) and the displacement of the focal point of theradiation source, the scanner control module 320 may send a controlsignal to the CT scanner 110. The CT scanner 110 may respond to thecontrol signal, and cause the radiation source 115 to emit radiation.During the radiation emission, the temperature of the radiation source115 may rise (e.g., by running the radiation source 115 originally at asleep mode or a low-load mode), or drop (e.g., by cooling the radiationsource 115 originally at an operative mode or a high-load mode). Thefocal point of the radiation source 115 may be displaced due to thermalexpansion or contraction accordingly.

At a time point B, the focal point of the radiation source 115 may bedisplaced to the focal point 902. A region R₂ of the detector 950 may beilluminated by the radiation emitted from the radiation source 115 atthe time point B. The focal point 902 is an arbitrary focal point of theradiation source 115 between the focal point 901 and the farthermostfocal point the radiation source 115 may ever have along the X directionor the Z direction.

In some embodiments, as illustrated in FIG. 9-A, to determine thedisplacement from the focal point 901 to the focal point 902, thecorrelation determination sub-module 344 may determine a distance xbetween the farther edge (indicated by line 961) of region R₂ (relativeto the focal point 901) and the intersection point of the surface of thedetector 950 and line 960. For example, to determine x, the correlationdetermination sub-module 344 may locate an illuminated (or notilluminated) detector unit locating at (approximately or precisely) thefarther edge of region R₂ based on the signals generated by the detectorunits. The detector unit locating at the farther edge of region R₂ maybe determined as the ith detector unit. The correlation determinationsub-module 344 may also locate the detector unit locating at(approximately or precisely) the intersection point, for example, basedon the structure information of the CT scanner 110. For instance, the CTscanner 110 may be configured that the focal point 901 is right above(approximately or precisely) a certain detector unit (e.g., detectorunit locating at the center of the detector 950) along the Y direction,and the related structure information may be pre-stored in a storagedevice (e.g., the storage 150, the storage 220, the storage 275, andmemory 280). The detector unit locating at the intersection point may bedetermined as the jth detector unit. The correlation determinationsub-module 344 may obtain x by multiplying the length (or averagelength) of the detector units with the absolute value of (j−i).Alternatively or additionally, the correlation determination sub-module344 may obtain x based on i, j (optional), and a look-up tablecorrelating x, i and j (optional).

The correlation determination sub-module 344 may then determine thedisplacement D from the focal point 901 to the focal point 902 viaEquation (3), which may be express as:

$\begin{matrix}{{D = {\left( {x - {\frac{d}{2}*\frac{\left( {H_{F2P} + H_{P2D}} \right)}{H_{F2P}}}} \right)*\frac{H_{F2P}}{H_{P2D}}}},} & (3)\end{matrix}$where H_(F2P) is the distance between the focal point 902 (or focalpoint 901 as the displacement along the Y direction is omitted) and thecentral plane (dashed line) of plate 910 along the Y direction, H_(P2D)is the distance between the central plane of the plate 910 and thedetector 950 along the Y direction, and d is the diameter of the pinhole915. H_(F2P), H_(P2D) and d may be provided with the CT scanner 110and/or plate 910, or be directly measured by a user.

Alternatively or additionally, the correlation determination sub-module344 may obtain D based on i, j (optional), and a look-up tablecorrelating D, i and j (optional).

In some embodiments, as illustrated in FIG. 9-B, to determine thedisplacement from the focal point 901 to the focal point 902, thecorrelation determination sub-module 344 may determine a distance x′between the centroid of region R₂ and the centroid of region R₁. Forexample, to determine x′, the correlation determination sub-module 344may determine the region R₂ and region R₁ and their relative position(e.g., the position of one of the region R₂ and region R₁ relative tothe position of the other) based on the signals generated by thedetector units and the structure information of the detector 950. Thecorrelation determination sub-module 344 may then determine thecentroids of region R₂ and region R₁ and the distance x′. Merely by wayof example, the correlation determination sub-module 344 may thendetermine the displacement D from the focal point 901 to the focal point902 according to Equation (4), which may be express as:

$\begin{matrix}{{D = {x^{\prime}*\frac{H_{F2P}}{H_{P2D}}}},} & (4)\end{matrix}$where H_(F2P) and H_(P2D) hold the same meaning as in Equation (3) andmay be obtained in a similar way.

Region R₃ is the common region shared by regions R₁ and R₂. During thedisplacement of the focal point from the focal point 901 to the focalpoint 902, region R₃ may always be illuminated. The non-uniform ASG (notshown in FIG. 9) of the detector 950 may be configured so that at leasta pair of first detector unit and second detector unit may locate withinthe region R₃. The signals generated by the first detector unit and thesecond detector unit may be extensively collected (e.g., 1˜500 samplesper second) during the displacement of the focal point between the focalpoints 901 and 902. A first intensity and a second intensity may beobtained by the correlation determination sub-module 344 at each of aplurality of predetermined time points. The correlation determinationsub-module 344 may also determine a displacement from the focal point901 to the current focal point at each of the plurality of predeterminedtime points (e.g., according to the exemplary method described above orin a similar manner). The correlation determination sub-module 344 maygenerate a correlation between a ratio of the first intensity to thesecond intensity and the displacement. The correlation may be in theform of one or more mathematical functions (e.g., by fitting), or alookup table (e.g., by recording). The generated correlation may bestored in a storage device (e.g., storage 150, storage 220, storage 275,memory 280) for further use. In 820 of process 800 illustrated in FIG.8, the focal point determination sub-module 342 may obtain thecorrelation from the storage device to determine the displacement of thefocal points.

In some embodiments, the determination of the correlation may beperformed during the acquisition of scan data by the CT scanner 110.

Having thus described the basic concepts, it may be rather apparent tothose skilled in the art after reading this detailed disclosure that theforegoing detailed disclosure is intended to be presented by way ofexample only and is not limiting. Various alterations, improvements, andmodifications may occur and are intended to those skilled in the art,though not expressly stated herein. These alterations, improvements, andmodifications are intended to be suggested by this disclosure, and arewithin the spirit and scope of the exemplary embodiments of thisdisclosure.

Moreover, certain terminology has been used to describe embodiments ofthe present disclosure. For example, the terms “one embodiment,” “anembodiment,” and/or “some embodiments” mean that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the present disclosure.

Further, it will be appreciated by one skilled in the art, aspects ofthe present disclosure may be illustrated and described herein in any ofa number of patentable classes or context including any new and usefulprocess, machine, manufacture, or composition of matter, or any new anduseful improvement thereof. Accordingly, aspects of the presentdisclosure may be implemented entirely hardware, entirely software(including firmware, resident software, micro-code) or combiningsoftware and hardware implementation that may all generally be referredto herein as a “unit,” “module,” or “system.” Furthermore, aspects ofthe present disclosure may take the form of a computer program productembodied in one or more computer readable media having computer readableprogram code embodied thereon.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including electro-magnetic, optical, or thelike, or any suitable combination thereof. A computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that may communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device. Program code embodied on acomputer readable signal medium may be transmitted using any appropriatemedium, including wireless, wireline, optical fiber cable, RF, or thelike, or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET,Python or the like, conventional procedural programming languages, suchas the “C” programming language, Visual Basic, Fortran 2103, Perl, COBOL2102, PHP, ABAP, dynamic programming languages such as Python, Ruby andGroovy, or other programming languages. The program code may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider) or in a cloud computing environment or offered as aservice such as a Software as a Service (SaaS).

Furthermore, the recited order of processing elements or sequences, orthe use of numbers, letters, or other designations therefore, is notintended to limit the claimed processes and methods to any order exceptas may be specified in the claims. Although the above disclosurediscusses through various examples what is currently considered to be avariety of useful embodiments of the disclosure, it is to be understoodthat such detail is solely for that purpose, and that the appendedclaims are not limited to the disclosed embodiments, but, on thecontrary, are intended to cover modifications and equivalentarrangements that are within the spirit and scope of the disclosedembodiments. For example, although the implementation of variouscomponents described above may be embodied in a hardware device, it mayalso be implemented as a software only solution, for example, aninstallation on an existing server or mobile device.

Similarly, it should be appreciated that in the foregoing description ofembodiments of the present disclosure, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure aiding in theunderstanding of one or more of the various inventive embodiments. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the claimed object matter requires more features than areexpressly recited in each claim. Rather, inventive embodiments lie inless than all features of a single foregoing disclosed embodiment.

In some embodiments, the numbers expressing quantities or propertiesused to describe and claim certain embodiments of the application are tobe understood as being modified in some instances by the term “about,”“approximate,” or “substantially.” For example, “about,” “approximate,”or “substantially” may indicate ±20% variation of the value itdescribes, unless otherwise stated. Accordingly, in some embodiments,the numerical parameters set forth in the written description andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by a particular embodiment. Insome embodiments, the numerical parameters should be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of some embodiments of the application areapproximations, the numerical values set forth in the specific examplesare reported as precisely as practicable.

Each of the patents, patent applications, publications of patentapplications, and other material, such as articles, books,specifications, publications, documents, things, and/or the like,referenced herein is hereby incorporated herein by this reference in itsentirety for all purposes, excepting any prosecution file historyassociated with same, any of same that is inconsistent with or inconflict with the present document, or any of same that may have alimiting affect as to the broadest scope of the claims now or laterassociated with the present document. By way of example, should there beany inconsistency or conflict between the description, definition,and/or the use of a term associated with any of the incorporatedmaterial and that associated with the present document, the description,definition, and/or the use of the term in the present document shallprevail.

In closing, it is to be understood that the embodiments of theapplication disclosed herein are illustrative of the principles of theembodiments of the application. Other modifications that may be employedmay be within the scope of the application. Thus, by way of example, butnot of limitation, alternative configurations of the embodiments of theapplication may be utilized in accordance with the teachings herein.Accordingly, embodiments of the present application are not limited tothat precisely as shown and described.

What is claimed is:
 1. A method implemented on at least one machine eachof which has at least one processor and a storage device, the methodcomprising: determining a first intensity of first radiation incident ona first detector unit of a scanner, the scanner including a non-uniformanti-scatter grid (ASG) and a radiation source, the non-uniform ASGbeing configured according to a first focal point of the radiationsource; determining a second intensity of second radiation incident on asecond detector unit of the scanner, wherein the first radiation and thesecond radiation are emitted from the radiation source with a secondfocal point; and determining a reference radiation intensity for atleast one of the first detector unit or the second detector unit;obtaining a first ratio of the first intensity to a first referenceradiation intensity for the first detector unit; obtaining a secondratio of the second intensity to a second reference radiation intensityfor the second detector unit: determining a direction of thedisplacement by comparing the first ratio and the second ratio; anddetermining a displacement of the second focal point from the firstfocal point based on the direction of the displacement.
 2. The method ofclaim 1, further comprising: obtaining at least one parameter relatingto the configuration of the ASG, wherein the at least one parameterincludes a height of at least a portion of the non-uniform ASG, a widthof the at least a portion of the non-uniform ASG, or a distance from thesecond focal point to the portion of the non-uniform ASG; anddetermining the displacement based on the at least one parameter.
 3. Themethod of claim 2, wherein the non-uniform ASG includes at least onefirst cell, and the first detector unit and the second detector unit areincluded in the at least one first cell.
 4. The method of claim 2,wherein the non-uniform ASG includes at least one second cell and atleast one third cell, the at least one second cell and the at least onethird cell include plates of different heights, the first detector unitis included in the at least one second cell, and the second detectorunit is included in the at least one third cell.
 5. The method of claim1, wherein the reference radiation intensity for at least one of thefirst detector unit or the second detector unit corresponds to anintensity of the radiation received by the first detector unit or thesecond detector when a focal point of the radiation source is at thefirst focal point.
 6. The method of claim 5, wherein the determining areference radiation intensity for at least one of the first detectorunit or the second detector unit comprising: obtaining a plurality offirst intensities and second intensities at different time points;determine, as the time the ASG aligned with the first focal point, atime point when a sum of a first intensity and a second intensityreaches maximum among the different time points; and determining thefirst intensity and the second intensity at the determined time point asthe reference radiation intensity for the first detector unit and thesecond detector respectively.
 7. The method of claim 6, furthercomprising: determining an average of the first intensity and the secondintensity at the determined time point as the reference radiationintensity for both of the first detector unit and the second detector.8. The method of claim 7, the first radiation and the second radiationbeing emitted during the obtaining the scan data.
 9. The method of claim1, further comprising: generating, based on the displacement, acalibration instruction for calibrating the scanner.
 10. The method ofclaim 1, further comprising: obtaining scan data by causing the scannerto scan a subject; and generating an image based on the scan data andthe displacement.
 11. A system, comprising at least one processor and atleast one storage for storing instructions, the instructions, whenexecuted by the at least one processor, causing the at least oneprocessor to: determine a first intensity of first radiation incident ona first detector unit of a scanner, the scanner including a non-uniformanti-scatter grid (ASG) and a radiation source, the non-uniform ASGbeing configured according to a first focal point of the radiationsource; determine a second intensity of second radiation incident on asecond detector unit of the scanner, wherein the first radiation and thesecond radiation are emitted from the radiation source with a secondfocal point; obtain a reference radiation intensity for at least one ofthe first detector unit or the second detector unit; obtaining a firstratio of the first intensity to a first reference radiation intensityfor the first detector unit; obtaining a second ratio of the secondintensity to a second reference radiation intensity for the seconddetector unit: determining a direction of the displacement by comparingthe first ratio and the second ratio; and determine a displacement ofthe second focal point from the first focal point based on the directionof the displacement.
 12. The system of claim 11, the at least oneprocessor is further configured to: obtain at least one parameterrelating to the configuration of the ASG, wherein the at least oneparameter includes a height of at least a portion of the non-uniformASG, a width of the at least a portion of the non-uniform ASG, or adistance from the second focal point to the portion of the non-uniformASG; and determine the displacement based on the at least one parameter.13. The system of claim 12, wherein the non-uniform ASG includes atleast one first cell, and the first detector unit and the seconddetector unit are included in the at least one first cell.
 14. Thesystem of claim 12, wherein the non-uniform ASG includes at least onesecond cell and at least one third cell, the at least one second celland the at least one third cell includes plates of different heights,the first detector unit is included in the at least one second cell, andthe second detector unit is included in the at least one third cell. 15.The system of claim 11, wherein the reference radiation intensity for atleast one of the first detector unit or the second detector unitcorresponds to an intensity of the radiation received by the firstdetector unit or the second detector when a focal point of the radiationsource is at the first focal point.
 16. The system of claim 15, whereinto obtain the reference radiation intensity for at least one of thefirst detector unit or the second detector unit, the at least oneprocessor is configured to: obtain a plurality of first intensities ofthe at least one of the first detector unit and a plurality of secondintensities of the at least one of the second detector unit at differenttime points; determine, as the time the ASG aligned with the first focalpoint, a time point when a sum of a first intensity and a secondintensity reaches maximum among the different time points; and determinethe first intensity and the second intensity at the determined timepoint as the reference radiation intensity for the at least one of thefirst detector unit and the at least one of the second detectorrespectively.
 17. The system of claim 16, the at least one processor isfurther configured to determine an average of the first intensity andthe second intensity at the determined time point as the referenceradiation intensity for both of the first detector unit and the seconddetector.
 18. The system of claim 11, the at least one processor isfurther configured to: generate, based on the displacement, acalibration instruction for calibrating the scanner.
 19. The system ofclaim 11, the at least one processor is further configured to: obtainscan data by causing the scanner to scan a subject, and generate animage based on the scan data and the displacement.
 20. A non-transitorycomputer readable medium, storing instructions, the instructions whenexecuted by a processor, causing the processor to execute operationscomprising: determining a first intensity of first radiation incident ona first detector unit of a scanner, the scanner including a non-uniformanti-scatter grid (ASG) and a radiation source, the non-uniform ASGbeing configured according to a first focal point of the radiationsource; determining a second intensity of second radiation incident on asecond detector unit of the scanner, wherein the first radiation and thesecond radiation are emitted from the radiation source with a secondfocal point; determining a reference radiation intensity for at leastone of the first detector unit or the second detector unit; obtaining afirst ratio of the first radiation intensity to a first referenceradiation intensity for the first detector unit; obtaining a secondratio of the second radiation intensity to a second reference radiationintensity for the second detector unit; and determining a direction ofthe displacement by comparing the first ratio and the second ratio; anddetermining a displacement of the second focal point from the firstfocal point based on the direction of the displacement.